MULLIN ET AL,: VERTICAL STRUCTURE OF PLANKTON OFF CALIFORNIA 



29 30 31 



Thunderstorm Rain' 



I 2 3 4 5 6 



I I I I I 



>C,Ji^, "■■^^  i^^ 



Wind 

 Direction 



N 

 W— I— E 



Rom 



Winds at Lindberg Field, San Diego 

 Winds at San Clemente Island 



[10 



m/sec 



<_) 2 - 



In Port 



O 

 o 





 17 

 16 



15 h 



Temperature Difference, Onn — 30nn, Dana Point 



1 1 1 1 1 1 r 



Mean Temperature, and 5m, 

 Dana Point x 



■In Port 



Mean Water Temperature, Scripps Pier, La Jolla 



2 - 



E I - 

 



Swell Height at Scripps _| 

 Pier, La Jollo 



I I I.I 



2 



e I 







IIMIIIIMII 



Significant Wave Height, 

 Oceanside 



lliiiiiiiilinilll 



29 30 31 ' I 2 3 4 5 6 



MARCH APRIL 



Figure l. — winds, water temperature, temperature gradient, 

 and wave height at Southern California locations during this 

 study. For temperature, dots are Dana Point, x's are La Jolla. 

 Wind direction is the direction from which the wind is blowing. 



note 3), and these differences were each significant 

 by rank sum test (P < 0.05). This is not what one 

 would expect from simple mixing, in which the 

 nearsurface isotherms should shoal and the 

 deeper isotherms deepen. 



A. Zooplanktonic Taxa and 

 Community Structure 



We examined statistically the data on zoo- 

 plankton summarized in the Appendix for 

 answers to several questions concerning temporal 

 changes in the distributions, using the ANOVA or 

 nonparametric tests summarized in Tables 1 and 

 2. Daytime vertical distributions of many of these 

 taxa off Southern California in late spring and fall 

 are given by Fiedler (1983). As noted in the tables, 

 there are potential ambiguities in the interpreta- 

 tion of even statistically significant results, such 

 as the difficulty in distinguishing diel migration of 

 a zooplanktonic taxon from a diel variation in its 

 capability to avoid capture by the pump. More 

 serious, and applicable to phytoplankton as well as 



zooplankton, is the impossibility of distinguish- 

 ing between 1) biological changes caused directly 

 by the storm (such as vertical redistribution, 

 changes in behavior, or changes in the balance 

 between birth and death of a taxon) and 2) storm- 

 driven advection into the area of water with 

 planktonic populations differing in abundances or 

 behavior from those present prior to the storm, but 

 neither the original nor the replacement popula- 

 tions having themselves changed in these proper- 

 ties. Advection undoubtedly occurred before, dur- 

 ing, and after the storm; the issue is whether 

 biologically caused changes associated with the 

 storm occurred as well. 



L Diel Vertical Migrations 



Based on results from ANOVA classification 1 

 (Table 1) or nonparametric Test 1 (Table 2), the 

 taxa migrating into the upper 50 m from deeper 

 water at night were the copepodites and adults of 

 Pleuromamma and Metridia. These are real mi- 

 grations, since sampling the water column of the 

 Southern California Bight to greater depths re- 

 veals a change in depth of maximal abundance 

 from below 100 m by day to within the upper 50 m 

 at night (Esterly 1912; Enright 1977; Brooks and 

 Mullin 1983). Euphausiid furcilia were also more 

 abundant at night than by day. 



Of the remaining zooplanktonic taxa (which did 

 not have significant diel variation in total abun- 

 dance within the upper 50 m), the populations of 

 female, CV, and CIII Calanus, euphausiid calyp- 

 topes, and cyphonautes larvae were centered sig- 

 nificantly higher at night than by day in the water 

 column. Again, these results are consistent with 

 results of sampling to greater depths in nearby 

 waters (Esterly 1912; Enright and Honegger 1977; 

 Mullin 1979; Brooks and Mullin 1983). Other taxa 

 probably belonging to this category of behavior 

 are adult Rhincalanus and Eucalanus (numbers 

 too small for reliability). Curiously, when tem- 

 poral changes are removed from the analysis 

 (ANOVA classification 3 (Table 1) ), female and CV 

 Calanus a-nd SiduXt Rhincalanus , Eucalanus, and 

 Metridia tend to be uniformly distributed in the 

 upper 50 m. 



2. Changes Following the Storm 



Several taxa were significantly different in 

 abundance following the passage of the storm 

 [ANOVA classification 2 (Table 1) or nonparamet- 

 ric Test 3 (Table 2)], and most of these were larval 



155 



